Solid pesticides intended for field dilution with liquids are usually sold in the form of emulsive concentrates, wettable powders, or flowable concentrates. Emulsive concentrates are solutions of a solid pesticide in an appropriate solvent. Usually such solvents are mineral oils, other hydrocarbons and chlorinated hydrocarbons. A surface active compound is also included in such concentrates. When the concentrate is diluted with water or other diluent by the user prior to field application, the surface active compound stabilizes the resulting emulsion.
Wettable powders consist of a pesticide mixed with various amounts of solid fillers such as clay, talc, etc. These powders also include a surface active material to improve their wetting properties. The end-user obtains the wettable powder in the form of a solid mixture. Water is added to this solid mixture in the field to form a suspension of solid pesticide in water suitable for application to crops.
The emulsive concentrate system is not always practical in that many solid pesticides are not soluble in common low-cost solvents. Wettable powders are objectionable in that the user frequently is subjected to contact with the concentrated powder as he dumps it from a container into a mixing apparatus. It is also difficult to measure the solid, wettable powders with the usual liquid measuring devices available to the average user.
Water-insoluble, solid pesticides are most conveniently handled as aqueous flowables. Flowables are concentrated suspensions of a solid pesticide in an aqueous system. In general, there will usually be in excess of 10%, sometimes even as high as 80%, solids in these systems. A flowable has the characteristics of a rather thick liquid; that is, it may be poured from a container and pumped and otherwise handled as a viscous liquid. The purchaser of a flowable merely has to open the container and pour the contents into his mixing tank. After diluting the flowable to the proper concentration with water, it is ready to apply. With an aqueous flowable there is no dust and no hydrocarbon solvent.
However, one significant problem arises with flowables. Many flowable users attempt to apply a flowable along with other pesticides, fertilizers and other soil additives simultaneously from the same apparatus. This apparatus is commonly a sprayer which consists of a mixing and holding tank and a nozzle or other orifice system for spraying the pesticide on intended organisms. The user often attempts to charge all these different materials to the mixing tank along with the necessary water. In most cases, a flowable concentrate will, when treated in such a way, convert to a "cottage-cheese"-type of solid floc which soon plugs the orifices or the spray nozzles. This floculation occurs because the flowable suspension is "broken" by the presence of the other materials added to the mixing tank.